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Cosmic Flows Mike Hudson U. Waterloo / IAP

Cosmic Flows Mike Hudson U. Waterloo / IAP. Our Local Group has a peculiar velocity of ~600 km/s with respect to the Cosmic Microwave Background. Tully et al ‘08 have shown that the LG’s motion is shared by the Local Sheet (<7 Mpc) - linear. What masses are the source of this motion?

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Cosmic Flows Mike Hudson U. Waterloo / IAP

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  1. Cosmic Flows Mike Hudson U. Waterloo / IAP

  2. Our Local Group has a peculiar velocity of ~600 km/s with respect to the Cosmic Microwave Background Tully et al ‘08 have shown that the LG’s motion is shared by the Local Sheet (<7 Mpc) - linear What masses are the source of this motion? On what scale is the Universe at rest?

  3. Outline • Two approaches: Direct: Peculiar velocity measurements Parametric: Density field predictions, and comparison to peculiar velocity measurements

  4. Mapping the Peculiar Velocity Field

  5. Mapping the Peculiar Velocity Field • The peculiar velocity of a single object (e.g. LG) cannot distinguish between a small nearby overdensity or a massive distant overdensity. • By mapping the peculiar velocity field, can find the d field: • Infall into an attractor suggests local source. • Coherent “bulk flow” with little shear suggests distant sources.

  6. Measuring peculiar velocities • cz = H0 r + vpec • Measuring redshifts (cz) is easy. • Measuring r is much more difficult, and less accurate. • Tully-Fisher (~20% uncertainty per gal) • Fundamental Plane (~20% uncertainty) • Type Ia SNe (~10% uncertainty)

  7. Bulk flow • The bulk flow is the average peculiar velocity over some volume. • Less noisy than individual measurements • It is sensitive to structures on scales larger than the scale being averaged.

  8. Some history… • Rubin et al. (‘76) detected a large bulk motion of Sc galaxies. • They assmed that Sc galaxies were standard candles. No dynamics (rotation curves or linewidths).

  9. Sayings of the Samurai • “A flow toward a great attractor centered on l=307, b=9 at a distance of 4350 km/s … gives a much better fit to the motions of the ellipticals than the bulk motion considered earlier.” • Lynden-Bell et al. 1988 “A mean motion of ellipticals toward l = 312 +-11 deg, b = 6 +- 10 deg at 599 +- 104 km/s is observed …. It is inferred that the Local Group motion with respect to the MWB is primarily due to mass concentrations at V greater than 5000 km/s.” Dressler et al. 1987

  10. Tidal Field in Local Surveys • Velocity from beyond • 60 h-1 Mpc • Mark III: • 366+/-125 km/s • SFI: 255 km/s • Hoffman, Eldar, Zaroubi & Dekel 2001

  11. Bulk Flows on Larger Scales • Measure bulk motion on scales larger than the distance to the GA, (hope to) separate local (GA) from distant sources. • However, recent (1999+) large-scale surveys measured bulk flow statistics that are apparently in conflict.

  12. ? No HST data HST snapshots (Laine et al 03) show filamentary dust in some BCGs. The L & P Smoking Gun? LP SMAC discussion in MH et al ‘04

  13. Bulk Flows in the CMB frame MH Analysis of Tonry et al. (2003) SNIa compilation

  14. Errors? • At this stage, many people attributed the discrepancies to putative systematic errors. • BUT quoted errors are for bulk flows of the sample, not of the volume and the large-scale surveys are sparse.

  15. SMAC EFAR Effects of Sparse Sampling SC Blue=In Red=Out GA PP

  16. Errors Including Sampling cf. Watkins & Feldman Sampling errors are not negligible

  17. With Feldman and Watkins, we have devised a new weighting scheme that minimizes small-scale aliasing • … See Hume’s talk for more details …

  18. Once we correct for sparse sampling, all of the peculiar velocity surveys agree with each other (except for Lauer & Postman’s BCG survey)

  19. Comparison SFI++ (Giovanelli et al) “DEEP” Various methods, clusters SMAC, Willick, EFAR, SC, SNe Bulk flow: 387 +- ~100 km/s towards l=295, b=10 • Tully-Fisher • in field • Bulk flow: • 430 +- ~90 km/s • towards • l=284, b=12 Combined: 407+- 81 km/s, towards l=287, b=8

  20. Combined cluster/Sne sample (excluding LP) Blue=In Red=Out Seven Samurai GA Bulk Flow: 387 +/- 80 km/s towards l=295, b=10 All surveys are consistent with this value

  21. Expectations for the Bulk Flow

  22. Consistency with LCDM Models What bulk flow do we expect for this combined sample? Allowing for the sparse sampling and assuming a flat LCDM power spectrum with WMAP5 parameters n=0.96, Wm h2= 0.13 and s8 ~0.8 then the cosmic r.m.s. is ~ 110 km/s. … but we measure 400 km/s. This model is then rejected at the 99% CL.

  23. Likelihood contours in Wm h2 vs s8 WMAP in colour; bulk flows in black. WMAP5 cosmology rejected at 2.5 s (98%). Watkins, Feldman and MH 2009

  24. Kinetic SZ effect • The kinetic SZ (kSZ) effect: the CMB temperature decrement will depend on the velocity of the cluster w.r.t to the CMB frame. • The signal depends on the amount of hot plasma in the cluster and the cluster’s line-of-sight velocity.

  25. Kashlinsky et al. 2008 • Kashlinsky et al. averaged the kSZ effect from 700 clusters within z < 0.3. • Their claim is that local volume out to ~900 Mpc/h was moving at a velocity 600-1000 km/s. • The direction of the flow that they find is within 6 deg of our result.

  26. Other probes • There are few independent ways to measure the fluctuations in the mass density on very large scales (~100 Mpc/h) in the nearby Universe. • Integrated Sachs-Wolfe effect (decay of potential) • SDSS galaxy power spectrum

  27. Integrated Sachs-Wolfe effect CDM predicts: A=1 Observed: A=2.23+-0.60

  28. Galaxy Power Spectra SDSS (more red gals) and 2dFGRS (more blue) disagree on small-scales. On large scales, they are expected to agree (and they do) … but both exceed LCDM predictions Percival et al 07 Scales probed by flows

  29. Future • Conventional distances indicator methods • running out of targets • NOAO FP Survey • SNe (infinite but slow) • kSZ ?

  30. NOAO Fundamental Plane Survey NOAO = National Optical Astronomical Observatories Picture: Kitt Peak,Arizona

  31. Conclusions I • Once sampling effects are considered no conflict between large-scale sparse peculiar velocity surveys (except possibly Lauer & Postman). • Combined sample bulk flow (~100 Mpc): • Combined: 407+- 81 km/s, towards l=287, b=8 • No convergence to CMB yet … • Not clear what is causing the flow. • Marginally inconsistent with LCDM (98%) • Some other measures also suggest large fluctuations on large scales.

  32. Predicting Peculiar Velocities using the Galaxy Density Field

  33. SC GA Mass vs Light SC GA PP PP Mass (Zaroubi inversion) (Far-infrared) Light (Branchini)

  34. “Biasing” • Averaged over large scales, one might assume that The simplest case is where b is the linear biasing parameter. but this need not be true: biasing might be non-linear and depend on other parameters

  35. Use galaxy dg=bd • Model external flows as bulk flow

  36. Comparison with 2MASS SNe Surface Brightness Fluctuations Pike & MH 05 Tully-Fisher For nearby peculiar velocity samples, 2MASS works well

  37. Measure from peculiar velocity surveys Cosmological Parameters Measure from clustering: s8,K =0.90 +- 0.10 s8,IRAS=0.85 +- 0.05

  38. Peculiar velocities yield • (/0.30)^0.55 = 0.80+- 0.05 • Compare with WMAP5 + BAO + SN : 0.78 +- 0.03 • …. No problem on small scales

  39. Residual Bulk Flow • With =0.5, Pike & Hudson (2005) found that • 271+- 104 km/s • in the direction l=300 b=15 • must arise from beyond 65 Mpc/h

  40. Predicted bulk flows from IRAS PSCz • If b=W0.6/b ~ 0.5, • additional sources (not included in PSCz) are required. • Beyond 200/h Mpc? • In the Zone of Avoidance? • Breakdown of linear biasing - extra mass in superclusters? Bulk flow in spheres Amplitude along l=300, b=10 “concordance direction” MH et al ‘04

  41. CosmographyWhat is the source of the large-scale ~300 km/s motion? • Must be beyond ~100 Mpc/h – • not the GA / Norma

  42. The Usual Suspects • The “Shapley Concentration” ? • fit indicates that 100 +/- 60 km/s of the LG’s motion is due to Shapley. • (implied mass ~ 5x1016 Msun for Wm=0.3). • Other structures such as the Horologium-Reticulum supercluster complex and large-scale voids may also play a role….

  43. Not much at Shapley Much stronger growth than in PSCz alone Growth of IRAS PSCz + Behind-the-Plane (BTP) Gravity Dipole Saunders et al. 2000 conference proceedings: astro-ph/ 0006005 … all that has been published so far. Predictions forb=1 If b~0.5, then >=300 km/s comes from beyond 100 Mpc

  44. X-ray-selected Cluster Dipole (Kocevski & Ebeling 2006) New all-sky X-ray selected catalogue shows a large jump (factor ~2 or ~300 km/s) at 150 h−1 Mpc. Much of this is due to the Shapley Concentration. VLG = Dcl Cluster dipole is NOT related to IRAS dipole by simple linear biasing

  45. Breakdown of Linear Biasing • In Shapley • IRAS PSCz: ~25 km/s at LG • Clusters: ~200-300 km/s at LG • Which is correct?

  46. Shapley Overdensity • Preliminary analysis of 6dF DR2 plus “Biasing” from mass-LK scaling relations. • Yields d ~ 1.75 on 30 Mpc scale. Compared with LCDM s30 ~ 0.25, this is a 7s fluctuation. • (Q for theorists: extreme tail of 1pt fcn?) • Infall “only” ~50-75 km/s at LG, but exceeding 1000 km/s in foreground.

  47. Density tracers suggest existence of large-scale structures, but do not agree on what the important structures are …

  48. Future • Deeper all-sky redshift surveys … 6dF + ? • Better treatments of “biasing” (halo model) • Better treatment of predicted peculiar velocities (e.g. MAK)

  49. Assume that there is a universal monotonic function which relates mass and light • M/L= U(M) Clusters Dwarfs Groups Galaxies Marinoni & Hudson 02 Steepest part of this diagram is around groups

  50. Conclusions II • Studies of the density field are consistent with the idea that much of the local velocity field arises due to sources at large distance • But what / where these sources are has not yet been determined.

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